1. Field
Exemplary embodiments of the present invention relate to a test mediation device and a system and method for testing a memory device, which are capable of increasing the yield of memory devices and reducing the test time.
2. Description of the Related Art
If fail occurs in a memory cell when fabricating memory devices, a repair process of enabling a redundancy circuit, which is included in a memory device treated as being failed, to be used is performed in order to repair the failed memory device. In general, a redundancy circuit includes a metallic fuse for storing fail information on a memory device, for example, the address of a fail memory cell, word line, or bit line, and the fuse is cut using a laser and the fail information is stored in the fuse in a repair process.
In general, this repair process of cutting a fuse using a laser and storing fail information is performed when a memory device is in a wafer state or a die state. This is because it is difficult to perform a laser test for detecting a fail memory cell of a memory device if the memory device is in a package state or a module state. For this reason, a test device, for example, a probe test device, for testing a memory device in a wafer state differs from a test device for testing a memory device in a package state or a module state in terms of a storage unit for storing information necessary when a test is performed.
A test device for testing a memory device in a wafer state is designed to determine whether a target test memory device has failed or not and store information for a repair process in order to perform the repair process for repairing a fail memory device. The information for the repair process includes information on the address of a fail memory cell or signal line, for example, a word line or a bit line, in the fail memory device. In contrast, the test device for testing a memory device in a package state or a module state is commonly designed not to store information for a repair process because the repair process is not accompanied.
Accordingly, if a memory device that has passed a test in a wafer state does not pass a test in a package state or a module state, the memory device cannot be repaired. In this case, there is a concern in that a repairable memory device may be treated as being a fail memory. In order to solve this concern, a method of toughly setting test conditions in a wafer state in order to prevent fail from occurring in a package state or a module state may be used. If test conditions are toughly set in a wafer state, however, the yield of memory devices may be very low and thus even a usable memory device may be treated as being failed.
A redundancy circuit for repairing a fail memory device may include an electrical fuse, for example, e-fuse, that is electrically cut in order to overcome a limit resulting from a metallic fuse that is cut by a laser. The e-fuse is a resistive element having a specific resistance value. When a very high current flows through the e-fuse, a state of the e-fuse is changed, for example, the e-fuse is cut, and thus the e-fuse has a different resistance value from the e-fuse before the current flows. If a redundancy circuit includes an e-fuse, there is an advantage in that a fail memory device may be repaired in a package state and a module state as well as in a wafer state because the fail memory device may be repaired even without using laser cutting.
An e-fuse may be cut even when a memory device is in a package state or a module state. As described above, however, a test device for testing a memory device in a package state or a module state is designed not to store information for a repair process. Accordingly, a repair process on a fail memory device in a package state or a module state is still restricted.
In order overcome the limit of a test device designed not to store information for a repair process as described above, a method of adding a storage circuit for storing information for repair to the test device or a method of designing new test equipment including a storage circuit for storing information for repair may be used. It may be difficult to use both the methods because the methods may require enormous investment costs.